A number of different instruments and devices are available to obtain the position of an underground cable. In some cases a coil is used to determine the magnitude of a current circulating through the cable. Such devices are not very accurate unless more than one coil is used and the position of the underground cable located by triangulation of more than one signal. One example of such a device is disclosed in Japanese patent application 55-51381. A similar instrument is disclosed in U.S. Pat. No. 5,093,622 to Balkman. A receiving array uses two vertically disposed sets of two orthogonal coils, each coil being a solenoid wound around a ferrite core.
Triangulation methods of determining the location of underground conductors generally require readings to be taken at different locations and a calculation must then be made from these readings to determine the location of the conductor. There are other types of instruments using radiated magnetic and electric fields to trace hidden conductors in open circuit and continuous circuit cases, see for example U.S. Pat. No. 4,686,454 to Pecukonis.